1. Field of the Invention
This invention is in the field of measurement of the various constituents of blood and, in one particular aspect, is related to the intra-corporeal measurement of the concentration of various blood constituents.
2. Description of Related Art
The prior art discloses a variety of sensors, probes and instruments used intra-corporeally for measuring blood parameters.
U.S. Pat. No. 4,682,895 to Costello discloses a fiber optic probe with a side sample chamber for intracorporeal insertion into blood vessels to measure various blood parameters. The side sample chamber includes a gap between two ends of a fiber optic and, necessarily, this side sample chamber assumes some singular disposition within a blood vessel.
Pending U.S. application Ser. No. 07/526,822 filed on May 22, 1990 by Costello et al. discloses a multi-sensor optical fiber probe for intra-corporeal insertion into blood vessels to measure various blood parameters. The probe may have a plurality of side sample chambers disposed at various positions about the circumference of the probe. In using the probe, one or more of the side sample chambers may be disposed near, directly adjacent, or in contact with a portion of the interior wall surface of a blood vessel.
U.S. Pat. No. 4,758,298 discloses a multi-sensor probe in which a plurality of fiber optics are bonded to each other. Sensing elements on each separate sensor are staggered in relation to each other. Each individual sensor is constructed with the sensing element between ends of optical fibers. In using the probe one or more of the sensing elements may be positioned near, directly adjacent, or in contact with a portion of the interior wall surface of an arterial cannula or blood vessel.
U.S. Pat. No. 4,830,013 discloses an in vivo blood parameter probe measurement system with one or more sensors at a distal end thereof. The probe is centrally moved back and forth in a catheter from a space filled with saline solution to a space filled with blood. One stated reason for keeping the probe centered within the catheter is to avoid the detrimental aspects of "wall effect." Wall effect occurs when a blood sensor's sensing element or area comes into contact with or in close proximity to a portion of the side wall of a blood vessel. Active metabolism of the cells of the blood vessel wall and/or the effects of restricted blood flow between the sensor(s) and the blood vessel wall can result in a microenvironment which is unlike that of the area of less restricted blood flow thus producing inaccurate measurements of the various blood parameters. Also, a probe may contact and sense wall tissue instead of blood. The method disclosed in U.S. Pat. No. 4,830,013 can result in erroneous results due to the undesirable mixing of infused saline solution and the blood being measured.
"Progress in the Development of a Fluorescent Intravascular Blood Gas System in Man," by Mahutte et al., 1989, discusses the deleterious effects of wall effect caused by a sensor touching a blood vessel wall and hence indicating a reading based in part on the nature of the tissue with which the sensor is in contact. A probe with three PO.sub.2 sensors distributed axially with two sensors located at different positions back from the probe tip was rotated 180 degrees to move one sensor away from the wall, but another sensor was then adversely affected by the wall effect. This reference teaches that a probe tip had to be retracted within an intra-arterial cannula tip to reduce the wall effect.
There is a need for a solution to the problem of blood parameter sensor disposition to avoid the detrimental effects of "wall effect." There is a need for a blood parameter sensor which produces accurate measurements from within the blood vessel without the need for maintaining the sensor within a artificial member such as a catheter.
Any unnecessary addition of instruments or structure into an area of blood flow is associated with the possibility of the production of undesirable thrombogenesis or clot formation. There is a need for methods and apparatuses for blood parameter sensing and measurement with which the level of thrombogenesis is reduced.